System Network Architecture (SNA) sub-area networks have been in extensive use since the early 1970's and at present form a major part of existing corporate and government networks. Sub-area networks are essentially hierarchical in nature. A host node, controlled primarily by IBM's Virtual Telecommunications Access Method (VTAM) controls all of the resources, message routing, resource location and access, etc. to other sub-area nodes within a domain. A domain is defined as a portion of a network consisting of one or many nodes and resources all of which are under the direct control of a VTAM at a host node for the domain.
More recently, IBM introduced its Advanced Peer-to-Peer Networking (APPN) architecture. APPN is fundamentally different from sub-area networks. An APPN network is made up of one or more network nodes (NN) and one or more end nodes (EN). Every NN can communicate with any other NN in an APPN network on a peer-to-peer basis. That is, there is no notion of a host that controls all of the resources of a domain. Every NN of an APPN network is equal in status to every other NN of the network. EN's, which are typically user terminals, printers and so on, are served by the NN's. Specifically, each EN is served by one NN. For example, if an application or user at an EN wishes to communicate with another application or user somewhere in the APPN network, the EN uses the resources of its serving NN to locate and communicate with the desired other application or user.
Because sub-area networks are in extensive use and will be so for many years to come, there is a need to provide ways for users to integrate their new APPN networks as they are introduced with their new or existing sub-area networks. One way of accomplishing this is by means of gateway nodes. U.S. Pat. No. 4,914,571 entitled LOCATING RESOURCES IN COMPUTER NETWORKS and issued to Baratz et al on Apr. 3, 1990 describes the methods of locating resources in an APPN network. U.S. Pat. No. 5,224,205, entitled METHOD OF COMBINING FLAT AND HIERARCHICALLY STRUCTURED COMPUTING NETWORKS INTO A SINGLE NETWORK and which issued to Dinkin et al on Jun. 29, 1993 describes algorithms performed at a gateway node for extending a search in an APPN network into a sub-area network. These patents are incorporated herein by reference in their entirety. Numerous other patents describe various inventions related to gateway functions interconnecting different networks. For example, U.S. Pat. No. 5,142,622, entitled A SYSTEM AND METHOD FOR INTERCONNECTING APPLICATIONS ACROSS DIFFERENT NETWORKS OF DATA PROCESSING SYSTEM issued to Owens on Aug. 25, 1992 and describes a gateway function for interconnecting TCP and sub-area networks. Additionally, routers also can be used to perform simpler and less flexible interconnections between networks of different types.
While all of these known methods of integrating networks provide great flexibility to network owners, additional capability is needed to increase further the utilization and integration of networks. This has the advantage of allowing the utilization of existing resources with new networking technologies and the resultant savings accompanying such enhanced integration.